people use it because its overpowered, no disadvantages at all. Broken animations and unrealistic insane reach that outranges pretty much all but the dedicated longspears. Human nature is to gravitate to the path of lease resistance and maximum reward.
change all 2h sword thrusts to polearm animation and then you'd actually see some diversity in 2h. its also fault of lazy, apathetic or incompetent devs/balance team. When swords account for 75% or more of 2h dmg/kills, something is wrong. For one, all unbalanced weapons probably need a weight increase of about 25-50% so they have chance to stun just about any sword or weapon in the game.
Every 2handed axe got a significant buff to damage last patch, Persian War Axes, Great Bardiche, etc all do around 50 cut damage now, I think it was across the board ~5 more damage? That was done in fact to make 2hands more diverse and popular. You shouldn't shit talk the devs when they are aware and just a few weeks ago addressed the issue with lots of bonus damage across the board to axes, which you conveniently forgot to mention.
Problem is most other 2handers besides the swords simply aren't very good. They are all unbalanced, short, slow, etc. On their own though, I think 38-41 or so cut damage that most top swords have simply isn't that powerful, when everyone is stacking armor. NA metagame has definitely shifted heavily in favor of long pierce weapons as far as polearms are concerned, capable of doing more damage in most scenarios than 2hands can. I feel like there are more shielders and spears than 2handers at most times as well, or at least a good balance of all melee.
2hand stab that everyone complains about gives you crippling weapon stun if you downblock it, good players take advantage of this at every opportunity. 2hand swords also do much less damage on their stabs than most polearms, so I think its balanced there.
I think instead of nerfs, more 2handers should just be added in that give more variety, something 1handers and polearms have a lot of. That is why I recently recommended dedicated thrusting 2handers be added here:
http://forum.meleegaming.com/game-balance-discussion/new-two-handed-thrusting-swords-estoc/Also if you play a lot of Strat battles, they really display a weakness of 2handers. Going into more coordinated, sustained line fighting with shield walls and pikes, 2handers can be at a big disadvantage, and are vulnerable to cav and ranged if they try to flank the formation. But getting past the pikewall and into their formation with a longsword, you can cause a quick burst of destruction that can help break the lines. Pretty realistic I'd say
